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ABR > Photon Therapy > Flashcards

Photon Therapy Flashcards

1
Q

In megavoltage photon beams, flatness and symmetry are usually defined at what depth?

A

10 cm

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2
Q

The mass energy absorption coefficient is related to what?

A

the amount of energy absorbed (Dose)

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3
Q

When we are attempting to perform a heterogeneity corrected calculation for 6 MV photons, which of the following parameters would be most useful?

The number of electrons per gram of the material

The number of electrons per cubic centimeter of the material

A

The number of electrons per cubic centimeter of the material

Compton scattering is related to the number of electrons per cubic centimeter.

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4
Q

The mass energy transfer coefficient is related to what?

A

Kerma

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5
Q

Suppose it was possible to adjust the SAD of an isocentric LINAC. Which of the following are true with regards to increasing the SAD.

Decreased beam divergence.
Increased Tissue Air Ratios (TAR)
Increased percent depth dose.
Decreased dose rate at isocenter.
Increased treatment SSDs.

A

Increased treatment SSDs.

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6
Q

Compared to a homogenous water phantom the dose at point C will be? (Water - Lung - Water)

A

Due to decreased attenuation in the lung, the dose beyond the inhomogeneity is expected to be greater.

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7
Q

Select all of the following items that affect geometric penumbra.

Source-Collimator Distance (SCD)
Source to Skin Distance (SSD)
Field Size
Source Size

A

Source-Collimator Distance (SCD)
Source to Skin Distance (SSD)
Source Size

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8
Q

Suppose you are treating a PA spinal field at an extended SSD of 135 cm to accommodate the area in question. Compared to a more standard setup at 100 cm SSD, the organs anterior to the cord are likely to receive…

A higher dose
A lower dose

A

As the SSD is increased, the PDD increases. Therefore, organs located anterior to what is being treated (deeper than the cord) will receive higher dose due to the increased PDD values. This occurs primarily due to inverse square differences in the falloff between the two geometries.

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9
Q

Electron density is most closely related to which of the following photon interaction types?

A

Compton Scattering

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10
Q

As an MV photon beam travels through lung the penumbra increases. True or False

A

True. Scattered electrons can travel farther in the low density lung which leads to an increase in penumbra. This is effect is worse for higher energies.

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11
Q

Compared to a homogenous water phantom, what do you expect the dose at point B to be? (Water to Lung to Water)

A

The dose within the lung is lower due to a lack of scatter within the lung as compared to water.

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12
Q

Divergent collimator jaws help to remove transmission penumbra.

A

True.

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13
Q

The density of lung relative to water is approximately what?

A

0.33

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14
Q

Which of the following would increase the penumbra associated with a Co-60 source?

Decrease the SSD.
Decrease the treatment depth.
Decrease the field size
Decrease the source size
Decrease the source collimator distance.

A

Excellent! All these options would tend to decrease the penumbra or have no effect with the exception of decreasing the source collimator distance.

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15
Q

Which of the following megavoltage photon energies would most likely demonstrate the largest penumbra?

10 MV

18 MV

20 MV

6 MV

A

Great! 20 MV should show the greatest amount of transmission penumbra and, therefore, the largest penumbra.

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16
Q

Over what percentage of a photon field size is flatness and symmetry usually defined?

A

80%

17
Q

Compared to a homogeneous water phantom, the dose at point B will be? (Water - Lung - Water)

A

Higher - Due to an increase in density there is increased scatter and attenuation leading to an increase in dose.

18
Q

A machine’s penumbra is generally defined as the distance between which two isodose curves?

A

Penumbra is usually defined as the distance between the 80% and 20% isodose lines.

19
Q

As the patient’s SSD increases, the measured %DD will also increase. True False

A

True - %DD has an inverse square component rolled in. Therefore, the farther from the source, the slower the falloff.

20
Q

Difference between gamma knife and cyber knife

A

CyberKnife can treat extracranially

21
Q

When measuring Sc,p for megavoltage photon fields, at what depth in water should your chamber be placed?

A

Reference depth

22
Q

You are treating a patient whose lesion is breaking through the skin surface. Which of the following should you recommend when treating with 6 MV photons.

Bolus
Wedge
Compensator

A

Bolus

23
Q

With regards to blocking an MV external beam field, which of the following will affect the dose under the block?

Block thickness.
Area of the block.
Area of unblocked field.
Energy of incident beam.

A

All

24
Q

Will the Field Size Correction Factor (FSCF) increase or decrease with increasing field size?

A

Increase

25
Q

The mid-line dose under a beam block can be calculated most accurately by using what?

A

Clarkson method

26
Q

A Treat-to is commonly used during SBRT treatments of the lung.

A

True - In Stereotactic Body Radiation Therapy (SBRT) for lung cancer, a “Treat-to” approach is often used because it allows for precise targeting of the tumor with high doses of radiation while minimizing damage to surrounding healthy tissue12. This precision is crucial in the lungs, where nearby structures like the heart and esophagus are sensitive to radiation.

27
Q

With regards to blocking an MV external beam field, which of the following will affect the dose under the block?

Block thickness.
Area of unblocked field.
Energy of incident beam.
Area of the block.
A

All

28
Q

Which of the following is not a method that has been utilized as a form of IMRT delivery?

Solid compensators

VMAT

Step and Shoot

Conformal Arc

Tomotherapy

Sliding Window

Peacock

A

Conformal Arc. Conformal Arc therapy simply takes the MLC’s and conforms them to the exterior border of the target to minimize treatment of healthy tissue. The field is always open and, therefore, this is not a method of IMRT delivery.

29
Q
A

ABR (3 decks)

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